Collecting activity information to evaluate therapy

ABSTRACT

A medical device delivers a therapy to a patient. The medical device or another device may periodically determine an activity level of the patient, and associate each determined activity level with a current therapy parameter set. A value of at least one activity metric is determined for each of a plurality of therapy parameter sets based on the activity levels associated with that therapy parameter set. A list of the therapy parameter sets is presented to a user, such as a clinician, for evaluation of the relative efficacy of the therapy parameter sets. The list may be ordered according to the one or more activity metric values to aid in evaluation of the therapy parameter sets. Where values are determined for a plurality of activity metrics, the list may be ordered according to the one of the activity metrics selected by the user.

This application is a continuation-in-part of U.S. application Ser. No. 10/825,965 now U.S. Pat. No. 7,395,113, filed Apr. 15, 2004, which claims the benefit of U.S. provisional application No. 60/553,778, filed Mar. 16, 2004. This application also claims the benefit of U.S. Provisional Application No. 60/785,658, filed Mar. 24, 2006. The entire content of each of these applications is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to medical devices and, more particularly, to medical devices that deliver therapy.

BACKGROUND

In some cases, an ailment may affect a patient's activity level or range of activities by preventing the patient from being active. For example, chronic pain may cause a patient to avoid particular physical activities, or physical activity in general, where such activities increase the pain experienced by the patient. Other ailments that may affect patient activity include movement disorders, such as tremor or Parkinson's disease, which may result in irregular movement or activity, as well as a generally decreased level of activity. Epilepsy is another example of a movement disorder that may change or otherwise affect physical activity frequency or magnitude of the patient. Occurring epileptic seizures, or the threat of seizures, may deter physical activity. Additional movement disorders that may change or otherwise affect physical activity include tremor, multiple sclerosis, or spasticity. The difficulty walking or otherwise moving experienced by patients with movement disorders may cause such patients to avoid movement to the extent possible.

Other neurological disorders may also affect patient activity. For example, mood or other psychological disorders may cause a patient to be less active and, particularly in the case of depression, listless. Example psychological disorders may include depression, mania, bipolar disorder, or obsessive-compulsive disorder. Furthermore, congestive heart failure and cardiac arrhythmia are other examples of disorders that may generally cause a patient to be less active

In some cases, these ailments are treated via a medical device, such as an implantable medical device (IMD). For example, patients may receive an implantable neurostimulator or drug delivery device to treat chronic pain, a movement disorder, a psychological disorder, or some other neurological disorder. Congestive heart failure and arrhythmia may be treated by, for example, a cardiac pacemaker or drug delivery device.

SUMMARY

In general, the invention is directed to techniques for evaluating a therapy delivered to a patient by a medical device based on patient activity. At any given time, the medical device delivers the therapy according to a current set of therapy parameters. The therapy parameters may change over time such that the therapy is delivered according to a plurality of different therapy parameter sets. The medical device, or another device, periodically determines an activity level of the patient, and associates each determined activity level with the current therapy parameter set. A value of at least one activity metric is determined for each of the therapy parameter sets based on the activity levels associated with that parameter set. A list of the therapy parameter sets and associated activity metrics is presented to a user, such as a clinician, for evaluation of the relative efficacy of the therapy parameter sets. The list may be ordered according to the activity metric values to aid in evaluation of the therapy parameter sets. In this manner, the user may readily identify the therapy parameter sets that support the highest activity levels for the patient, and evaluate the relative efficacy of the parameter sets.

The therapy delivering medical device or another device may monitor at least one signal that is generated by a sensor and varies as a function of patient activity. For example, the device may monitor a signal generated by an accelerometer, a bonded piezoelectric crystal, a mercury switch, or a gyro. In some embodiments, the device may monitor a signal that indicates a physiological parameter of the patient, which in turn varies as a function of patient activity. For example, the device may monitor a signal that indicates the heart rate, electrocardiogram (ECG) morphology, respiration rate, respiratory volume, core temperature, subcutaneous temperature, or muscular activity of the patient.

The therapy delivering medical device or another device may periodically determine an activity level of the patient based on the one or more signals. In some embodiments, the device periodically determines a number of activity counts based on the signals, and the number of activity counts is stored as the activity level. The number of activity counts may be a number of threshold crossings by a signal generated by a sensor such as an accelerometer or piezoelectric crystal during a sample period, or a number of switch contacts indicated by the signal generated by a sensor such as mercury switch during a sample period.

In some embodiments, the device may periodically determine a heart rate, measured value of one or more ECG morphological features, respiration rate, respiratory volume, core temperature, subcutaneous temperature, and/or muscular activity level of the patient based on one or more signals. The determined values of these parameters may be mean or median values. The device may compare a determined value of such a physiological parameter to one or more thresholds to determine a number of activity counts, which may be stored as a determined activity level. In other embodiments, the device may store the determined physiological parameter value as a determined activity level.

The use of activity counts, however, may allow the device to determine an activity level based on a plurality of signals. For example, the device may determine a first number of activity counts based on an accelerometer signal and a second number of activity counts based on a heart rate determined at the time the accelerometer signal was sampled. The device may determine an activity level by calculating the sum or average, which may be a weighted sum or average, of first and second activity counts.

As mentioned above, the device may associate each determined activity level with a current set of therapy parameters and, for each of a plurality of therapy parameter sets used by the medical device over time, a value of one or more activity metrics is determined. An activity metric value may be, for example, a mean or median activity level, such as an average number of activity counts per unit time. In other embodiments, an activity metric value may be chosen from a predetermined scale of activity metric values based on comparison of a mean or median activity level to one or more threshold values. The scale may be numeric, such as activity metric values from 1-10, or qualitative, such as low, medium or high activity.

In some embodiments, each activity level associated with a therapy parameter set is compared with the one or more thresholds, and percentages of time above and/or below the thresholds are determined as one or more activity metric values for that therapy parameter set. In other embodiments, each activity level associated with a therapy parameter set is compared with a threshold, and an average length of time that consecutively determined activity levels remain above the threshold is determined as an activity metric value for that therapy parameter set. One or both of the medical device or another device, such as a programming device or other computing device, may determine the activity metric values as described herein.

The computing device or, in some external medical device embodiments, the medical device, presents a list of the plurality of parameter sets and associated activity metric values via a display. The computing device may order the list according to the activity metric values. Where values are determined for a plurality of activity metrics for each of the therapy parameter sets, the computing device may order the list according to the values of a user selected one of the activity metrics. The computing device may also present other activity information to a user, such as a trend diagram of activity over time, or a histogram or pie chart illustrating percentages of time that activity levels were within certain ranges. The computing device may generate such charts or diagrams using activity levels associated with a particular one of the therapy parameter sets, or all of the determined activity levels.

In one embodiment, the invention is directed to a method that includes monitoring a signal that varies as a function of patient activity and periodically determining an activity level of the patient based on the signal. The method also includes associating each of the determined activity levels with a therapy parameter set currently used by a medical device to deliver a therapy to a patient when the activity level is determined, wherein the therapy comprises at least one of a movement disorder therapy, mood disorder therapy, or deep brain stimulation and determining a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets.

In another embodiment, the invention is directed to a medical system that includes a medical device that delivers at least one of a movement disorder therapy, mood disorder therapy, or deep brain stimulation to a patient. The medical system also includes a processor that monitors a signal that varies as a function of patient activity, periodically determines an activity level of the patient based on the signal, associates each of the determined activity levels with a therapy parameter set currently used by the medical device to deliver the at least one of the movement disorder therapy, mood disorder therapy, or deep brain stimulation to the patient when the activity level is determined, and determines a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets.

In another embodiment, the invention is directed to a medical system that includes means for delivering at least one of a movement disorder therapy, mood disorder therapy, or deep brain stimulation to a patient, means for monitoring a signal that varies as a function of patient activity, and means for periodically determining an activity level of the patient based on the signal. The medical system also includes means for associating each of the determined activity levels with a therapy parameter set currently used by the means for delivering to deliver the at least one of the movement disorder therapy, mood disorder therapy, or deep brain stimulation to a patient when the activity level is determined and means for determining a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets.

In an additional embodiment, the invention is directed to monitoring a signal generated by an implanted sensor that varies as a function of patient activity, detecting a plurality of gait freeze events based on the signal, and associating each of the gait freeze events with a therapy parameter set currently used by a medical device to deliver at least one of a Parkinson's disease therapy, epilepsy therapy, or deep brain stimulation to a patient.

In another additional embodiment, the invention is directed to a medical device that delivers at least one of a Parkinson's disease therapy, epilepsy therapy, or deep brain stimulation to a patient and an implanted sensor that generates a signal that varies as a function of activity of the patient. The medical device includes a processor that monitors the signal, detects a plurality of gait freeze events based on the signal, and associates each of the gait freeze events with a therapy parameter set currently used by the medical to deliver at least one of Parkinson's disease therapy, epilepsy therapy, or deep brain stimulation.

The invention is capable of providing one or more advantages. For example, a medical system according to the invention may provide a clinician with an objective indication of the efficacy of different sets of therapy parameters. Further, by displaying therapy parameter sets and associated activity metric values in an ordered and, in some cases, sortable list, the medical system may allow the clinician to more easily compare the relative efficacies of a plurality of therapy parameter sets. The medical system may be particularly useful in the context of trial neurostimulation, where the patient is encouraged to try a plurality of therapy parameter sets to allow the patient and clinician to identify efficacious therapy parameter sets. Further, the medical system may be particularly useful in the context of movement disorders, which may impact both the overall level of patient activity, and also result in irregular movements with activity.

The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are conceptual diagrams illustrating an example systems that includes an implantable medical device that collects activity information according to the invention.

FIGS. 2A and 2B are block diagrams further illustrating the example systems and implantable medical devices of FIGS. 1A and 1B.

FIG. 3 is a logic diagram illustrating an example circuit that detects the sleep state of a patient from the electroencephalogram (EEG) signal.

FIG. 4 is a block diagram illustrating an example memory of the implantable medical device of FIGS. 1A and 1B.

FIG. 5 is a flow diagram illustrating an example method for collecting activity information that may be employed by an implantable medical device.

FIG. 6 is a block diagram illustrating an example clinician programmer.

FIG. 7 illustrates an example list of therapy parameter sets and associated activity metric values that may be presented by a clinician programmer.

FIG. 8 is a flow diagram illustrating an example method for displaying a list of therapy parameter sets and associated activity metric values that may be employed by a clinician programmer.

FIG. 9 is a conceptual diagram illustrating a monitor that monitors values of one or more physiological parameters of the patient.

FIG. 10 is a conceptual diagram illustrating a monitor that monitors values of one or more accelerometers of the patient instead of, or in addition to, a therapy delivering medical device.

FIG. 11 is a flow diagram illustrating monitoring the heart rate and breathing rate of a patient by measuring cerebral spinal fluid pressure.

DETAILED DESCRIPTION

FIGS. 1A and 1B are conceptual diagrams illustrating example systems 10A and 10B (collectively “systems 10”) that respectively include an implantable medical device (IMD) 14A or 14B (collectively “IMDs 14”) that collect information relating to the activity of a respective one of patients 12A and 12B (collectively “patients 12”). In the illustrated example systems 10, IMDs 14 takes the form of an implantable neurostimulator that delivers neurostimulation therapy in the form of electrical pulses to patients 12. However, the invention is not limited to implementation via an implantable neurostimulator. For example, in some embodiments of the invention, IMDs 14 may take the form of an implantable pump or implantable cardiac rhythm management device, such as a pacemaker, that collect activity information. Further, the invention is not limited to implementation via an IMD. In other words, any implantable or external devices may collect activity information according to the invention.

In the illustrated example systems 10, IMDs 14 delivers neurostimulation therapy to patients 12 via leads 16A and 16B, and leads 16C and 16D (collectively “leads 16”), respectively. Leads 16A and 16B may, as shown in FIG. 1A, be implanted proximate to the spinal cord 18 of patient 12A, and IMD 14A may deliver spinal cord stimulation (SCS) therapy to patient 12A in order to, for example, reduce pain experienced by patient 12A. However, the invention is not limited to the configuration of leads 16 shown in FIG. 1A or the delivery of SCS or other pain therapies.

For example, in another embodiment, illustrated in FIG. 1B, leads 16C and 16D may extend to brain 19 of patient 12B, e.g., through cranium 17 of patient. IMD 14B may deliver deep brain stimulation (DBS) or cortical stimulation therapy to patient 12 to treat any of a variety of non-respiratory neurological disorders, such as movement disorders or psychological disorders. Non-respiratory neurological disorders generally exclude respiratory disorders, such as sleep apnea. Example therapies may treat tremor, Parkinson's disease, spasticity, epilepsy, depression or obsessive-compulsive disorder. As illustrated in FIG. 1B, leads 16C and 16D may be coupled to IMD 14B via one or more lead extensions 15.

As further examples, one or more leads 16 may be implanted proximate to the pelvic nerves (not shown) or stomach (not shown), and an IMD 14 may deliver neurostimulation therapy to treat incontinence or gastroparesis. Additionally, leads 16 may be implanted on or within the heart to treat any of a variety of cardiac disorders, such as congestive heart failure or arrhythmia, or may be implanted proximate to any peripheral nerves to treat any of a variety of disorders, such as peripheral neuropathy or other types of chronic pain.

The illustrated numbers and locations of leads 16 are merely examples. Embodiments of the invention may include any number of lead implanted at any of a variety of locations within a patient. Furthermore, the illustrated number and location of IMDs 14 are merely examples. IMDs 14 may be located anywhere within patient according to various embodiments of the invention. For example, in some embodiments, an IMD 14 may be implanted on or within cranium 17 for delivery of therapy to brain 19, or other structure of the head of the patient 12.

IMDs 14 deliver therapy according to a set of therapy parameters, i.e., a set of values for a number of parameters that define the therapy delivered according to that therapy parameter set. In embodiments where IMDs 14 deliver neurostimulation therapy in the form of electrical pulses, the parameters for each therapy parameter set may include voltage or current pulse amplitudes, pulse widths, pulse rates, duration, duty cycle and the like. Further, each of leads 16 includes electrodes (not shown in FIG. 1A or 1B), and a therapy parameter set may include information identifying which electrodes have been selected for delivery of pulses, and the polarities of the selected electrodes. In embodiments in which IMDs 14 deliver other types of therapies, therapy parameter sets may include other therapy parameters such as drug concentration and drug flow rate in the case of drug delivery therapy. Therapy parameter sets used by IMDs 14 may include a number of parameter sets programmed by a clinician (not shown), and parameter sets representing adjustments made by patients 12 to these preprogrammed sets.

IMDs 14 may deliver electrical stimulation to treat and/or reduce the symptoms of any of a variety of non-respiratory neurological disorders (hereinafter referred to as only “neurological disorders”). These neurological disorders may not include respiratory disorders, such as central sleep apnea. For example, IMDs 14 may deliver DBS in order to, for example, reduce the frequency and severity of epileptic seizures experienced by patients 12 with epilepsy. As other examples, IMDs 14 may deliver DBS in order to reduce the symptoms of a movement disorder or psychological disorder, such as tremor, Parkinson's disease, multiple sclerosis, spasticity, depression, mania, bipolar disorder, or obsessive-compulsive disorder. Additionally, IMDs 14 may deliver SCS to treat chronic pain or other non-respiratory neurological disorders, e.g., excluding for example central sleep apnea. Further, IMDs 14 may deliver stimulation to locations other than the spinal cord or brain to treat such disorders, or may deliver stimulation to the spinal cord or brain to treat other disorders.

Systems 10 also include a clinician programmer 20 (illustrated as part of system 10A in FIG. 1A). The clinician may use clinician programmer 20 to program therapy for patient 12A, e.g., specify a number of therapy parameter sets and provide the parameter sets to IMD 14A. The clinician may also use clinician programmer 20 to retrieve information collected by IMD 14A. The clinician may use clinician programmer 20 to communicate with IMD 14A both during initial programming of IMD 14A, and for collection of information and further programming during follow-up visits.

Clinician programmer 20 may, as shown in FIG. 1A, be a handheld computing device. Clinician programmer 20 includes a display 22, such as a LCD or LED display, to display information to a user. Clinician programmer 20 may also include a keypad 24, which may be used by a user to interact with clinician programmer 20. In some embodiments, display 22 may be a touch screen display, and a user may interact with clinician programmer 20 via display 22. A user may also interact with clinician programmer 20 using peripheral pointing devices, such as a stylus or mouse. Keypad 24 may take the form of an alphanumeric keypad or a reduced set of keys associated with particular functions.

Systems 10 also includes a patient programmer 26 (illustrated as part of system 10A in FIG. 1A), which also may, as shown in FIG. 1A, be a handheld computing device. Patient 12A may use patient programmer 26 to control the delivery of therapy by IMD 14A. For example, using patient programmer 26, patient 12A may select a current therapy parameter set from among the therapy parameter sets preprogrammed by the clinician, or may adjust one or more parameters of a preprogrammed therapy parameter set to arrive at the current therapy parameter set.

Patient programmer 26 may include a display 28 and a keypad 30, to allow patient 12A to interact with patient programmer 26. In some embodiments, display 28 may be a touch screen display, and patient 12A may interact with patient programmer 26 via display 28. Patient 12A may also interact with patient programmer 26 using peripheral pointing devices, such as a stylus, mouse, or the like.

Clinician and patient programmers 20, 26 are not limited to the hand-held computer embodiments illustrated in FIG. 1A. Programmers 20, 26 according to the invention may be any sort of computing device. For example, a programmer 20, 26 according to the invention may be a tablet-based computing device, a desktop computing device, or a workstation.

IMDs 14, clinician programmer 20 and patient programmer 26 may, as shown in FIG. 1A, communicate via wireless communication. Clinician programmer 20 and patient programmer 26 may, for example, communicate via wireless communication with IMD 14A using radio frequency (RF) or infrared telemetry techniques known in the art. Clinician programmer 20 and patient programmer 26 may communicate with each other using any of a variety of local wireless communication techniques, such as RF communication according to the 802.11 or Bluetooth specification sets, infrared communication according to the IRDA specification set, or other standard or proprietary telemetry protocols.

Clinician programmer 20 and patient programmer 26 need not communicate wirelessly, however. For example, programmers 20 and 26 may communicate via a wired connection, such as via a serial communication cable, or via exchange of removable media, such as magnetic or optical disks, or memory cards or sticks. Further, clinician programmer 20 may communicate with one or both of IMD 14 and patient programmer 26 via remote telemetry techniques known in the art, communicating via a local area network (LAN), wide area network (WAN), public switched telephone network (PSTN), or cellular telephone network, for example.

As mentioned above, IMDs 14 collect patient activity information. Specifically, as will be described in greater detail below, IMDs 14 may periodically determine an activity level of a patient 12 based on a signal that varies as a function of patient activity. IMDs 14 may associate each determined activity level with the therapy parameter set that is currently active when the activity level is determined. An activity level may comprise, for example, a number of activity counts, or a value for a physiological parameter that reflects patient activity.

Over time, IMDs 14 use a plurality of therapy parameter sets to deliver the therapy to a patient 12. A processor within IMDs 14 or another device, such as one of programmers 20, 26 or another computing device, determines a value of one or more activity metrics for each of the plurality of therapy parameter sets based on the activity levels associated with the therapy parameter sets. An activity metric value may be, for example, a mean or median activity level, such as an average number of activity counts per unit time. In other embodiments, an activity metric value may be chosen from a predetermined scale of activity metric values based on a comparison of a mean or median activity level to one or more threshold values. The scale may be numeric, such as activity metric values from 1-10, or qualitative, such as low, medium or high activity.

In some embodiments, each activity level associated with a therapy parameter set is compared with the one or more thresholds, and percentages of time above and/or below the thresholds are determined as one or more activity metric values for that therapy parameter set. In other embodiments, each activity level associated with a therapy parameter set is compared with a threshold, and an average length of time that consecutively determined activity levels remain above the threshold is determined as an activity metric value for that therapy parameter set.

In some embodiments, a plurality of activity metric values are determined for each of the plurality of therapy parameter sets. In such embodiments, an overall activity metric value may be determined. For example, the plurality of individual activity metric values may be used as indices to identify an overall activity metric value from a look-up table. The overall activity metric may selected from a predetermined scale of activity metric values, which may be numeric, such as activity metric values from 1-10, or qualitative, such as low, medium or high activity.

One or more of IMDs 14, programmers 20, 26, or another computing device may determine the activity metric values as described herein. In some embodiments, IMDs 14 determine and stores activity metric values for each of a plurality of therapy parameter sets, and provide information identifying the therapy parameter sets and the associated activity metric values to clinician programmer 20. In other embodiments, IMDs 14 provide information identifying the therapy parameter sets and associated activity levels to clinician programmer 20, and clinician programmer 20 determines the activity metric values for each of the therapy parameter sets.

In either of these embodiments, clinician programmer 20 presents a list of the plurality of parameter sets and associated activity metric values to the clinician via display 22. Programmer 20 may order the list according to the activity metric values. Where values are determined for a plurality of activity metrics for each of the therapy parameter sets, programmer 20 may order the list according to the values of one of the activity metrics that is selected by the clinician. Programmer 20 may also present other activity information to the clinician, such as a trend diagram of activity over time, or a histogram or pie chart illustrating percentages of time that activity levels were within certain ranges. Programmer 20 may generate such charts or diagrams using activity levels associated with a particular one of the therapy parameter sets, or all of the activity levels determined by IMDs 14.

However, the invention is not limited to embodiments that include programmer 20, or embodiments in which programmer 20 presents activity information to the clinician. For example, in some embodiments, programmer 26 presents activity information as described herein to one or both of the clinician and a patient 12. Further, in some embodiments, an external medical device comprises a display. In such embodiments, the external medical device may both determine activity metric values for the plurality of therapy parameter sets, and present the list of therapy parameter sets and activity metric values. Additionally, in some embodiments, any type of computing device, e.g., personal computer, workstation, or server, may identify activity levels, determine activity metric values, and/or present a list to a patient or clinician.

Further, the invention is not limited to embodiments in which a medical device determines activity levels. For example, in some embodiments, IMDs 14 may instead periodically record samples of one or more signals that vary as a function of patient activity, and associated the samples with a current therapy parameter set. In such embodiments, programmer 20 or 26, or another computing device, may receive information identifying a plurality of therapy parameter sets and the samples associated with the parameter sets, may determine activity levels based on the samples, and may determine one or more activity metric values for each of the therapy parameter sets based on the determined activity levels.

FIGS. 2A and 2B are block diagrams further illustrating systems 10A and 10B. In particular, FIG. 2A illustrates an example configuration of IMD 14A and leads 16A and 16B. FIG. 2B illustrates an example configuration of IMD 14B and leads 16C and 16D. FIGS. 2A and 2B also illustrate sensors 40A and 40B (collectively “sensors 40”) that generate signals that vary as a function of patient activity. As will be described in greater detail below, IMDs 14 monitors the signals, and may periodically determine an activity level based on the signals.

IMD 14A may deliver neurostimulation therapy via electrodes 42A-D of lead 16A and electrodes 42E-H of lead 16B, while IMD 14B delivers neurostimulation via electrodes 421-L of lead 16C and electrodes 42 M-P of lead 16D (collectively “electrodes 42”). Electrodes 42 may be ring electrodes. The configuration, type and number of electrodes 42 illustrated in FIGS. 2A and 2B are merely exemplary. For example, leads 16 may each include eight electrodes 42, and the electrodes 42 need not be arranged linearly on each of leads 16.

In each of systems 10A and 10B, electrodes 42 are electrically coupled to a therapy delivery module 44 via leads 16. Therapy delivery module 44 may, for example, include an output pulse generator coupled to a power source such as a battery. Therapy delivery module 44 may deliver electrical pulses to a patient 12 via at least some of electrodes 42 under the control of a processor 46, which controls therapy delivery module 44 to deliver neurostimulation therapy according to a current therapy parameter set. However, the invention is not limited to implantable neurostimulator embodiments or even to IMDs that deliver electrical stimulation. For example, in some embodiments a therapy delivery module 44 of an IMD may include a pump, circuitry to control the pump, and a reservoir to store a therapeutic agent for delivery via the pump.

Processor 46 may include a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), discrete logic circuitry, or the like. Memory 48 may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, and the like. In some embodiments, memory 48 stores program instructions that, when executed by processor 46, cause IMD 14 and processor 46 to perform the functions attributed to them herein.

Each of sensors 40 generates a signal that varies as a function of patient activity. IMDs 14 may include circuitry (not shown) that conditions the signals generated by sensors 40 such that they may be analyzed by processor 46. For example, IMDs 14 may include one or more analog to digital converters to convert analog signals generated by sensors 40 into digital signals usable by processor 46, as well as suitable filter and amplifier circuitry. Although shown as including two sensors 40, systems 10 may include any number of sensors.

Further, as illustrated in FIGS. 2A and 2B, sensors 40 may be included as part of IMDs 14, or coupled to IMDs 14 via leads 16. Sensors 40 may be coupled to IMDs 14 via therapy leads 16A-16D, or via other leads 16, such as lead 16E depicted in FIGS. 2A and 2B. In some embodiments, a sensor 40 located outside of an IMD 14 may be in wireless communication with processor 46. Wireless communication between sensors 40 and IMDs 14 may, as examples, include RF communication or communication via electrical signals conducted through the tissue and/or fluid of a patient 12.

A sensor 40 may be, for example, an accelerometer, a bonded piezoelectric crystal, a mercury switch, or a gyro that generates a signal as a function of patient activity, e.g., body motion, footfalls or other impact events, and the like. Processor 46 may determine an activity level based on a signal generated by one of these types of sensors 40 by sampling the signal and determining a number of activity counts during the sample period. Processor 46 may then store the determined number of activity counts in memory 48 as an activity level.

For example, processor 46 may compare the sample of a signal generated by an accelerometer or piezoelectric crystal to one or more amplitude thresholds stored within memory 48. Processor 46 may identify each threshold crossing as an activity count. Where processor 46 compares the sample to multiple thresholds with varying amplitudes, processor 46 may identify crossing of higher amplitude thresholds as multiple activity counts. Using multiple thresholds to identify activity counts, processor 46 may be able to more accurately determine the extent of patient activity for both high impact, low frequency and low impact, high frequency activities. In embodiments in which a sensor 40 takes the form of a mercury switch, processor 46 may identify the number of switch contacts indicated during the sample period as the number of activity counts.

In embodiments in which a sensor 40 comprises an accelerometer or piezoelectric crystal, IMDs 14 may include a filter (not shown), or processor 46 may apply a digital filter, that passes a band from approximately 0.1 Hz to 10 Hz. The filter may reduce noise in the signal, and pass the portion of the signal that reflects patient activity.

In some embodiments, sensors 40 may generate a signal both as a function of patient activity and patient posture. For example, accelerometers, gyros, or magnetometers may generate signals that indicate both the activity and the posture of a patient 12. In some embodiments, in order to identify posture, sensors 40 such as accelerometers may be oriented substantially orthogonally with respect to each other. In addition to being oriented orthogonally with respect to each other, each of sensors 40 used to detect the posture of a patient 12 may be substantially aligned with an axis of the body of a patient 12. When accelerometers, for example, are aligned in this manner, the magnitude and polarity of DC components of the signals generate by the accelerometers indicate the orientation of the patient relative to the Earth's gravity, e.g., the posture of a patient 12. Further information regarding use of orthogonally aligned accelerometers to determine patient posture may be found in a commonly assigned U.S. Pat. No. 5,593,431, which issued to Todd J. Sheldon.

Other sensors 40 that may generate a signal that indicates the posture of a patient 12 include electrodes that generate a signal as a function of electrical activity within muscles of a patient 12, e.g., an electromyogram (EMG) signal, or a bonded piezoelectric crystal that generates a signal as a function of contraction of muscles. Electrodes or bonded piezoelectric crystals may be implanted in the legs, buttocks, chest, abdomen, or back of a patient 12, and coupled to IMDs 14 wirelessly or via one or more leads 16. Alternatively, electrodes may be integrated in a housing of the IMD or piezoelectric crystals may be bonded to the housing when IMD is implanted in the buttocks, chest, abdomen, or back of a patient 12. The signals generated by such sensors when implanted in these locations may vary based on the posture of a patient 12, e.g., may vary based on whether the patient is standing, sitting, or laying down.

Further, the posture of a patient 12 may affect the thoracic impedance of the patient. Consequently, sensors 40 may include an electrode pair, including one electrode integrated with the housing of IMDs 14 and one of electrodes 42, that generates a signal as a function of the thoracic impedance of a patient 12, and processor 46 may detect the posture or posture changes of a patient 12 based on the signal. The electrodes of the pair may be located on opposite sides of the patient's thorax. For example, the electrode pair may include one of electrodes 42 located proximate to the spine of a patient for delivery of SCS therapy, and IMDs 14 with an electrode integrated in its housing may be implanted in the abdomen or chest of a patient 12. As another example, IMDs 14 may include electrodes or other sensors 40 implanted to detect thoracic impedance in addition to leads 16 implanted within the brain of a patient 12.

Additionally, changes of the posture of a patient 12 may cause pressure changes with the cerebrospinal fluid (CSF) of the patient. Consequently, sensors 40 may include pressure sensors coupled to one or more intrathecal or intracerebroventricular catheters, or pressure sensors coupled to IMDs 14 wirelessly or via lead 16. CSF pressure changes associated with posture changes may be particularly evident within the brain of the patient, e.g., may be particularly apparent in an intracranial pressure (ICP) waveform.

In some embodiments, processor 46 may monitor a signal that indicates a physiological parameter of a patient 12, which in turn varies as a function of patient activity. For example, processor 46 may monitor a signal that indicates the heart rate, ECG morphology, EEG morphology, respiration rate, respiratory volume, core temperature, subcutaneous temperature, or muscular activity of the patient. In such embodiments, processor 46 may periodically determine the heart rate, measured value of one or more ECG morphological features, respiration rate, respiratory volume, core temperature, subcutaneous temperature, or muscular activity level of a patient 12 based on the signal. The determined values of these parameters may be mean or median values.

Sensors 40 may include electrodes located on leads 16 or integrated as part of the housing of IMDs 14 that generates an electrogram signal as a function of electrical activity of the heart of a patient 12, and processor 46 may periodically determine the heart rate of the patient 12 based on the electrogram signal. In other embodiments, a sensor 40 may include an acoustic sensor within IMDs 14, a pressure sensor within the bloodstream or cerebrospinal fluid of a patient 12, or a temperature sensor located within the bloodstream of the patient 12. The signals generated by such sensors 40 may vary as a function of contraction of the heart of a patient 12, and can be used by processor 46 to periodically determine the heart rate of the patient 12.

In some embodiments, processor 46 may detect, and measure values for one or more ECG morphological features within an electrogram generated by electrodes as described above. ECG morphological features may vary in a manner that indicates the activity level of patient. For example, the amplitude of the ST segment of the ECG may increase with increased patient activity. Further, the amplitude of QRS complex or T-wave may increase, and the widths of the QRS complex and T-wave may decrease with increased patient activity. The QT interval and the latency of an evoked response may decrease with increased patient activity, and the amplitude of the evoked response may increase with increased patient activity.

In some embodiments, sensors 40 may include an electrode pair, including one electrode integrated with the housing of IMDs 14 and one of electrodes 42, as described above. In such embodiments, the electrode pair may generate a signal as a function of the thoracic impedance of a patient 12, which varies as a function of respiration by the patient 12. In other embodiments, sensors 40 may include a strain gauge, bonded piezoelectric element, or pressure sensor within the blood or cerebrospinal fluid that generates a signal that varies based on patient respiration. Processor 46 may monitor the signals generated by such sensors 40 to periodically determine a respiration rate and/or respiratory volume of a patient 12. An electrogram generated by electrodes as discussed above may also be modulated by patient respiration, and processor 46 may use the electrogram as an indirect representation of respiration rate.

In some embodiments, sensors 40 may include one or more electrodes that generate an electromyogram (EMG) signal as a function of muscle electrical activity. The amplitude and/or frequency of an EMG signal may vary based on the activity level of a patient. The electrodes may be, for example, located in the legs, abdomen, chest, back or buttocks of a patient 12 to detect muscle activity associated with walking, running, or the like. The electrodes may be coupled to IMDs 14 wirelessly or by leads 16 or, if IMDs 14 is implanted in these locations, integrated with a housing of IMDs 14.

However, bonded piezoelectric crystals located in these areas generate signals as a function of muscle contraction in addition to body motion, footfalls or other impact events. Consequently, use of bonded piezoelectric crystals to detect activity of a patient 12 may be preferred in some embodiments in which it is desired to detect muscle activity in addition to body motion, footfalls, or other impact events. Bonded piezoelectric crystals may be coupled to IMDs 14 wirelessly or via leads 16, or piezoelectric crystals may be bonded to the can of IMDs 14 when the IMD is implanted in these areas, e.g., in the back, chest buttocks or abdomen of a patient 12.

In alternative embodiments, sensors 40 may be configured for placement within or around the brain of a patient 12 to detect the onset, magnitude, or duration of a neurological disorder. For example, sensors 40 may detect the onset of an epileptic seizure and track the duration and extent of the seizure. IMDs 14 may compare neurological events to physical activity to determine how the neurological events affect physical activity. IMDs 14 may also initiate or change electrical stimulation when a neurological event is detected.

Further, sensors 40 may include any of a variety of known temperature sensors to generate a signal as a function of a core or subcutaneous temperature of a patient 12. Core or subcutaneous temperature may vary as a function of the activity level of a patient 12. Such temperature sensors may be incorporated within the housing of IMDs 14, or coupled to IMDs 14 wirelessly or via leads.

In some embodiments, processor 46 compares a determined value of such a physiological parameter to one or more thresholds or a look-up table stored in memory to determine a number of activity counts, and stores the determined number of activity counts in memory 48 as a determined activity level. In other embodiments, processor 46 may store the determined physiological parameter value as a determined activity level. The use of activity counts, however, may allow processor 46 to determine an activity level based on a plurality of signals generated by a plurality of sensors 40. For example, processor 46 may determine a first number of activity counts based on a sample of an accelerometer signal and a second number of activity counts based on a heart rate determined from an electrogram signal at the time the accelerometer signal was sampled. Processor 46 may determine an activity level by calculating the sum or average, which may be a weighted sum or average, of first and second activity counts.

Processor 46 may record activity levels continuously or periodically, e.g., one sample every minute or continuously for ten minutes each hour. In some embodiments, processor 46 limits recording of activity levels to relevant time periods, i.e., when a patient 12 is awake or likely to be awake, and therefore likely to be active. For example, patient may indicate via patient programmer 26 when patient is going to sleep or awake. Processor 46 may receive these indications via a telemetry circuit 50 of IMDs 14, and may suspend or resume recording of activity levels based on the indications. In other embodiments, processor 46 may maintain a real-time clock, and may record activity levels based on the time of day indicated by the clock, e.g., processor 46 may limit activity level recording to daytime hours.

In some embodiments, processor 46 may monitor one or more physiological parameters of a patient 12 via signals generated by sensors 40, and may determine when the patient 12 is attempting to sleep or asleep based on the physiological parameters. For example, processor 46 may determine when a patient 12 is attempting to sleep by receiving an indication from patient programmer 26, or by monitoring the posture of the patient 12 to determine when the patient 12 is recumbent. Sensors 40 may include a plurality of orthogonally arranged accelerometers, as discussed above, and processor 46 may monitor the DC components of the signals generated by the accelerometers to determine when patient is recumbent.

In other embodiments, processor 46 determines when a patient 12 is attempting to fall asleep based on the level of melatonin in a bodily fluid. In such embodiments, a sensor 40 may take the form of a chemical sensor that is sensitive to the level of melatonin or a metabolite of melatonin in the bodily fluid, and estimate the time that a patient 12 will attempt to fall asleep based on the detection. For example, processor 46 may compare the melatonin level or rate of change in the melatonin level to a threshold level stored in memory 48, and identify the time that threshold value is exceeded. Processor 46 may identify the time that a patient 12 is attempting to fall asleep as the time that the threshold is exceeded, or some amount of time after the threshold is exceeded. Any of a variety of combinations or variations of the above-described techniques may be used to determine when a patient 12 is attempting to fall asleep, and a specific one or more techniques may be selected based on the sleeping and activity habits of a particular patient.

In order to determine whether a patient 12 is asleep, processor 46 may monitor any one or more physiological parameters that discernibly change when the patient 12 falls asleep, such as activity level, posture, heart rate, ECG morphology, respiration rate, respiratory volume, blood pressure, blood oxygen saturation, partial pressure of oxygen within blood, partial pressure of oxygen within cerebrospinal fluid, muscular activity and tone, core temperature, subcutaneous temperature, arterial blood flow, brain electrical activity, eye motion, and galvanic skin response. Processor 46 may additionally or alternatively monitor the variability of one or more of these physiological parameters, such as heart rate and respiration rate, which may discernible change when a patient 12 is asleep. Further details regarding monitoring physiological parameters to identify when a patient is attempting to sleep and when the patient is asleep may be found in a commonly-assigned and co-pending U.S. patent application Ser. No. 11/691,405 by Kenneth Heruth and Keith Miesel, entitled “DETECTING SLEEP,” which was assigned and filed Mar. 26, 2007, and is incorporated herein by reference in its entirety.

For example, in some embodiments, processor 46 may determine whether a patient 12 is asleep by analyzing an electroencephalogram (EEG) signal from the patient. EEG analysis is not limited to embodiments which include leads 16 implanted on or within brain 19 of patient. Nonetheless, system 10B, illustrated in FIGS. 1B and 2B, is an example of a system that includes electrodes 42, located on or within the brain of patient 12B, that are coupled to IMD 14B. As shown in FIG. 2B, electrodes 42 may be selectively coupled to therapy module 44 or an EEG signal module 54 by a multiplexer 52, which operates under the control of processor 46. EEG signal module 54 receives signals from a selected set of the electrodes 42 via multiplexer 52 as controlled by processor 46. EEG signal module 54 may analyze the EEG signal for certain features indicative of sleep or different sleep states, and provide indications of relating to sleep or sleep states to processor 46. Thus, electrodes 42 and EEG signal module 54 may be considered another sensor 40 in system 10B. IMD 14B may include circuitry (not shown) that conditions the EEG signal such that it may be analyzed by processor 52. For example, IMD 14B may include one or more analog to digital converters to convert analog signals received from electrodes 42 into digital signals usable by processor 46, as well as suitable filter and amplifier circuitry.

Processor 46 may direct EEG signal module to analyze the EEG signal to determine whether patient 12B is sleeping, and such analysis may be considered alone or in combination with other physiological parameters to determine whether patient 12B is asleep. EEG signal module 60 may process the EEG signals to detect when patient 12 is asleep using any of a variety of techniques, such as techniques that identify whether a patient is asleep based on the amplitude and/or frequency of the EEG signals. In some embodiments, the functionality of EEG signal module 54 may be provided by processor 46, which, as described above, may include one or more microprocessors, ASICs, or the like.

In other embodiments, processor 46 may record activity levels in response to receiving an indication from a patient 12 via patient programmer 26. For example, processor 46 may record activity levels during times when a patient 12 believes the therapy delivered by IMDs 14 is ineffective and/or the symptoms experienced by the patient 12 have worsened. In this manner, processor 46 may limit data collection to periods in which more probative data is likely to be collected, and thereby conserve a battery and/or storage space within memory 48.

Further, as described above, the invention is not limited to embodiments in which IMDs 14 determines activity levels. In some embodiments, processor 46 may periodically store samples of the signals generated by sensors 40 in memory 48, rather than activity levels, and may associate those samples with the current therapy parameter set.

FIG. 3 is a logical diagram of an example circuit that detects sleep and/or the sleep type of a patient based on the electroencephalogram (EEG) signal. Alternatively, the circuit may detect an awake state when the patient is not in any sleep state. As shown in FIG. 3, module 49 may be integrated into an EEG signal module of IMDs 14 or a separate implantable or external device capable of detecting an EEG signal. An EEG signal detected by electrodes adjacent to the brain of a patent 12 is transmitted into module 49 and provided to three channels, each of which includes a respective one of amplifiers 51, 67 and 83, and bandpass filters 53, 69 and 85. In other embodiments, a common amplifier amplifies the EEG signal prior to filters 53, 69 and 85.

Bandpass filter 53 allows frequencies between approximately 4 Hz and approximately 8 Hz, and signals within the frequency range may be prevalent in the EEG during S1 and S2 sleep states. Bandpass filter 69 allows frequencies between approximately 1 Hz and approximately 3 Hz, which may be prevalent in the EEG during the S3 and S4 sleep states. Bandpass filter 85 allows frequencies between approximately 10 Hz and approximately 50 Hz, which may be prevalent in the EEG during REM sleep. Each resulting signal may then be processed to identify in which sleep state patient 12 is.

After bandpass filtering of the original EEG signal, the filtered signals are similarly processed in parallel before being delivered to sleep logic module 99. For ease of discussion, only one of the three channels will be discussed herein, but each of the filtered signals would be processed similarly.

Once the EEG signal is filtered by bandpass filter 53, the signal is rectified by full-wave rectifier 55. Modules 57 and 59 respectively determine the foreground average and background average so that the current energy level can be compared to a background level at comparator 63. The signal from background average is increased by gain 61 before being sent to comparator 63, because comparator 63 operates in the range of millivolts or volts while the EEG signal amplitude is originally on the order of microvolts. The signal from comparator 63 is indicative of sleep stages S1 and S2. If duration logic 65 determines that the signal is greater than a predetermined level for a predetermined amount of time, the signal is sent to sleep logic module 99 indicating that a patient 12 may be within the S1 or S2 sleep states. In some embodiments, as least duration logic 65, 81, 97 and sleep logic 99 may be embodied in a processor of the device containing EEG module 49.

Module 49 may detect all sleep types for a patient 12. Further, the beginning of sleep may be detected by module 49 based on the sleep state of a patient 12. Some of the components of module 49 may vary from the example of FIG. 3. For example, gains 61, 77 and 93 may be provided from the same power source. Module 49 may be embodied as analog circuitry, digital circuitry, or a combination thereof.

In other embodiments, FIG. 3 may not need to reference the background average to determine the current state of sleep of a patient 12. Instead, the power of the signals from bandpass filters 53, 69 and 85 are compared to each other, and sleep logic module 99 determines which the sleep state of a patient 12 based upon the frequency band that has the highest power. In this case, the signals from full-wave rectifiers 55, 71 and 87 are sent directly to a device that calculates the signal power, such as a spectral power distribution module (SPD), and then to sleep logic module 99 which determines the frequency band of the greatest power, e.g., the sleep state of a patient 12. In some cases, the signal from full-wave rectifiers 55, 71 and 87 may be normalized by a gain component to correctly weight each frequency band.

FIG. 4 illustrates memory 48 of IMDs 14 in greater detail. As shown in FIG. 4, memory 48 stores information describing a plurality of therapy parameter sets 60. Therapy parameter sets 60 may include parameter sets specified by a clinician using clinician programmer 20. Therapy parameter sets 60 may also include parameter sets that are the result of a patient 12 changing one or more parameters of one of the preprogrammed therapy parameter sets. For example, a patient 12 may change parameters such as pulse amplitude, frequency or pulse width via patient programmer 26.

Memory 48 also stores the activity levels 62 determined by processor 46. When processor 46 determines an activity level as discussed above, processor 46 associates the determined activity level with the current one of therapy parameter sets 60, e.g., the one of therapy parameter sets 60 that processor 46 is currently using to control delivery of therapy by therapy module 44 to a patient 12. For example, processor 46 may store determined activity levels 62 within memory 48 with an indication of the parameter sets 60 with which they are associated. In other embodiments, processor 46 stores samples (not shown) of signals generated by sensors 40 within memory 48 with an indication of the parameter sets 60 with which they are associated.

In some embodiments, processor 46 determines a value of one or more activity metrics for each of therapy parameter sets 60 based on the activity levels 62 associated with the parameter sets 60. Processor 46 may store the determined activity metric values 66 within memory 48 with an indication as to which of therapy parameter sets 60 the determined values are associated with. For example, processor 46 may determine a mean or median of activity levels associated with a therapy parameter set, and store the mean or median activity level as an activity metric value 66 for the therapy parameter set.

In embodiments in which activity levels 62 comprise activity counts, processor 46 may store, for example, an average number of activity counts per unit time as an activity metric value. An average number of activity counts over a period substantially between ten and sixty minutes, for example, may provide a more accurate indication of activity than an average over shorter periods by ameliorating the effect of transient activities on an activity signal or physiological parameters. For example, rolling over in bed may briefly increase the amplitude of an activity signal and a heart rate, thereby confounding the activity analysis.

In other embodiments, processor 46 may compare a mean or median activity level to one or more threshold values 64, and may select an activity metric value from a predetermined scale of activity metric values based on the comparison. The scale may be numeric, such as activity metric values from 1-10, or qualitative, such as low, medium or high activity. The scale of activity metric values may be, for example, stored as a look-up table within memory 48. Processor 46 stores the activity metric value 66 selected from the scale within memory 48.

In some embodiments, processor 46 compares each activity level 62 associated with a therapy parameter set 60 to one or more threshold values 64. Based on the comparison, processor 46 may determine percentages of time above and/or below the thresholds, or within threshold ranges. Processor 46 may store the one or more determined percentages within memory 48 as one or more activity metric values 66 for that therapy parameter set. In other embodiments, processor 46 compares each activity level 62 associated with a therapy parameter set 66 to a threshold values 64, and determines an average length of time that consecutively recorded activity levels 62 remained above the threshold as an activity metric value 66 for that therapy parameter set.

In some embodiments, processor 46 determines a plurality of activity metric values for each of the plurality of therapy parameter sets, and determines an overall activity metric value for a parameter set based on the values of the individual activity metrics for that parameter set. For example, processor 46 may use the plurality of individual activity metric values as indices to identify an overall activity metric value from a look-up table stored in memory 48. Processor 46 may select the overall metric value from a predetermined scale of activity metric values, which may be numeric, such as activity metric values from 1-10, or qualitative, such as low, medium or high activity.

As shown in FIGS. 2A and 2B, IMDs 14 include a telemetry circuit 50, and processor 46 communicates with programmers 20, 26 via telemetry circuit 50. In some embodiments, processor 46 provides information identifying therapy parameter sets 60 and activity metric values 66 associated with the parameter sets to programmer 20, and programmer 20 displays a list of therapy parameter sets 60 and associated activity metric values 66. In other embodiments, as will be described in greater detail below, processor 46 does not determine activity metric values 66. Instead, processor 46 provides activity levels 62 to programmer 20 via telemetry circuit 50, and programmer 20 determines activity metric values 66 for display to the clinician. Further, in other embodiments, processor 46 provides samples of signals generated by sensors 40 to programmer 20 via telemetry circuit 50, and programmer 20 may determine both activity levels 62 and activity metric values 66 based on the samples. Some external medical device embodiments of the invention include a display, and a processor of such an external medical device may both determine activity metric values 66 and display a list of therapy parameter sets 60 and associated activity metric values 66 to a clinician.

FIG. 5 is a flow diagram illustrating an example method for collecting activity information that may be employed by IMDs 14. An IMD 14 monitors one or more activity signals (70). For example, an IMD 14 may monitor a signal generated by an accelerometer or piezoelectric crystal, and/or a signal that indicates a physiological parameter that varies as a function of patient activity, such heart rate, ECG morphology, respiration rate, respiratory volume, core temperature, subcutaneous temperature, or muscle activity.

An IMD 14 determines an activity level 62 (72). For example, an IMD 14 may determine a number of activity counts based on the one or more signals, as described above. An IMD 14 identifies the current therapy parameter set 60, and associates the determined activity level 62 with the current therapy parameter set 60 (74). For example, an IMD 14 may store the determined activity level 62 in memory 48 with an indication of the current therapy parameter set 60. An IMD 14 may then update one or more activity metric values 66 associated with the current therapy parameter set 60, as described above (76).

An IMD 14 may periodically perform the example method illustrated in FIG. 5, e.g., may periodically monitor the activity signal (70), determine activity levels 62 (72), and associate the determined activity levels 62 with a current therapy parameter set 60 (74). As described above, an IMD 14 may only perform the example method during daytime hours, or when patient is awake and not attempting to sleep, and/or only in response to an indication received from a patient 12 via patient programmer 20. An IMD 14 need not update activity metric values 66 each time an activity level 62 is determined. In some embodiments, for example, an IMD 14 may store activity levels 62 within memory, and may determine the activity metric values 66 upon receiving a request for the values from clinician programmer 20. In alternative examples, an IMD 14 may associate activity levels 62 and/or detection of neurological events with a current therapy parameter set 60. In addition, a patient 12 may manually input the occurrence of a neurological event for use by an IMD 14.

Further, in some embodiments, as will be described in greater detail below, IMDs 14 do not determine the activity metric values 66, but instead provide activity levels 62 to a computing device, such as clinician programmer 20 or patient programmer 26. In such embodiments, the computing device determines the activity metric values 66 associated with each of the therapy parameter sets 60. Additionally, as described above, IMDs 14 need not determine activity levels 62, but may instead store samples of the signals generated by sensors 40. In such embodiments, the computing device may determine both activity levels 62 and activity metric values 66 based on the samples.

FIG. 6 is a block diagram illustrating clinician programmer 20. A clinician may interact with a processor 80 via a user interface 82 in order to program therapy for patient 12, e.g., specify therapy parameter sets. Processor 80 may provide the specified therapy parameter sets to IMDs 14 via telemetry circuit 84.

At another time, e.g., during a follow up visit, processor 80 may receive information identifying a plurality of therapy parameter sets 60 from IMDs 14 via telemetry circuit 84, which may be stored in a memory 86. The therapy parameter sets 60 may include the originally specified parameter sets, and parameter sets resulting from manipulation of one or more therapy parameters by a patient 12 using patient programmer 26. In some embodiments, processor 80 also receives activity metric values 66 associated with the therapy parameter sets 60, and stores the activity metric values in memory 86.

In other embodiments, processor 80 receives activity levels 62 associated with the therapy parameter sets 60, and determines values 66 of one or more activity metrics for each of the plurality of therapy parameter sets 60 using any of the techniques described above with reference to IMDs 14 and FIGS. 2A, 2B and 4. Processor 80 may, for example, use threshold values 64 stored in memory 86 to determine activity metric values 66, as described above. In still other embodiments, processor 80 receives samples of activity signals from IMDs 14, and determines activity levels 62 and activity metric values 66 based on signals using any of the techniques described above with reference to IMDs 14 and FIGS. 2A, 2B, and 4.

Upon receiving or determining activity metric values 66, processor 80 generates a list of the therapy parameter sets 60 and associated activity metric values 66, and presents the list to the clinician. User interface 82 may include display 22, and processor 80 may display the list via display 22. The list of therapy parameter sets 60 may be ordered according to the associated activity metric values 66. Where a plurality of activity metric values are associated with each of the parameter sets, the list may be ordered according to the values of the activity metric selected by the clinician. Processor 80 may also present other activity information to a user, such as a trend diagram of activity over time, or a histogram, pie chart, or other illustration of percentages of time that activity levels 62 were within certain ranges. Processor 80 may generate such charts or diagrams using activity levels 62 associated with a particular one of the therapy parameter sets 66, or all of the activity levels 62 recorded by IMDs 14.

User interface 82 may include display 22 and keypad 24, and may also include a touch screen or peripheral pointing devices as described above. Processor 80 may include a microprocessor, a controller, a DSP, an ASIC, an FPGA, discrete logic circuitry, or the like. Memory 86 may include program instructions that, when executed by processor 80, cause clinician programmer 20 to perform the functions ascribed to clinician programmer 20 herein. Memory 86 may include any volatile, non-volatile, fixed, removable, magnetic, optical, or electrical media, such as a RAM, ROM, CD-ROM, hard disk, removable magnetic disk, memory cards or sticks, NVRAM, EEPROM, flash memory, and the like.

FIG. 7 illustrates an example list 90 of therapy parameter sets and associated activity metric values 66 that may be presented by clinician programmer 20. Each row of example list 90 includes an identification of one of therapy parameter sets 60, the parameters of the therapy parameter set, and values 66 associated with the therapy parameter set for each of two illustrated activity metrics. Programmer 20 may order list 90 according to a user-selected one of the activity metrics.

The activity metrics illustrated in FIG. 7 are a percentage of time active, and an average number of activity counts per hour. IMDs 14 or programmer 20 may determine the average number of activity counts per hour for one of the illustrated therapy parameter sets by identifying the total number of activity counts associated with the parameter set and the total amount of time that IMDs 14 was using the parameter set. IMDs 14 or programmer 20 may determine the percentage of time active for one of parameter sets 60 by comparing each activity level 62 associated with the parameter set to an “active” threshold, and determining the percentage of activity levels 62 above the threshold. As illustrated in FIG. 7, IMDs 14 or programmer 20 may also compare each activity level for the therapy parameter set to an additional, “high activity” threshold, and determine a percentage of activity levels 62 above that threshold.

FIG. 8 is a flow diagram illustrating an example method for displaying a list of therapy parameter sets 60 and associated activity metric values 66 that may be employed by a clinician programmer 20. Programmer 20 receives information identifying therapy parameter sets 60 and associated activity levels 62 from an IMD 14 (100). Programmer 20 then determines one or more activity metric values 66 for each of the therapy parameter sets based on the activity levels 62 associated with the therapy parameter sets (102). In other embodiments, an IMD 14 determines the activity metric values 66, and provides them to programmer 20, or provides samples of activity signals associated with therapy parameter sets to programmer 20 for determination of activity metric values, as described above. After receiving or determining activity metric values 66, programmer 20 presents a list 90 of therapy parameter sets 60 and associated activity metric values 66 to the clinician, e.g., via display 22 (104). Programmer 20 may order list 90 of therapy parameter sets 60 according to the associated activity metric values 66, and the clinician may select which of a plurality of activity metrics list 90 is ordered according to via a user interface 82 (106).

As discussed above, the overall activity level of a patient, e.g., the extent to which the patient is on his or her feet and moving or otherwise active, rather than sitting or lying in place, may be negatively impacted by any of a variety of ailments or symptoms. Accordingly, the activity level of a patient may reflect the efficacy of a particular therapy or therapy parameter set in treating the ailment or symptom. In other words, it may generally be the case that the more efficacious a therapy parameter set is, the more active the patient will be. In addition, the activity level of a patient may reflect the efficacy of particular values for therapy parameters.

As discussed above, in accordance with the invention, activity levels may be monitored during delivery of therapy according to a plurality of therapy parameter sets, and used to evaluate the efficacy of the therapy parameter sets. As an example chronic pain may cause a patient to avoid particular activities, high levels of activity, or activity in general. Systems according to the invention may include any of a variety of medical devices that deliver any of a variety of therapies to treat chronic pain, such as SCS, DBS, cranial nerve stimulation, peripheral nerve stimulation, or one or more drugs. Systems may use the techniques of the invention described above to associate activity levels and metrics with therapy parameter sets for delivery of such therapies, and thereby evaluate the extent to which a therapy parameter set is alleviating chronic pain by evaluating the extent to which the therapy parameter set improves the overall activity level of the patient.

As another example, mood disorders, and particularly depression, may cause a patient to be inactive, despite a physical ability to be active. Often, a patient with depression will spend the significant majority of his or her day in bed. Systems according to the invention may include any of a variety of medical devices that deliver any of a variety of therapies to treat a mood disorder, such as DBS, cranial nerve stimulation, peripheral nerve stimulation, vagal nerve stimulation, or one or more drugs. Systems may use the techniques of the invention described above to associate activity levels and metrics with therapy parameter sets for delivery of such therapies, and thereby evaluate the extent to which a therapy parameter set is alleviating the mood disorder by evaluating the extent to which the therapy parameter set improves the overall activity level of the patient.

Movement disorders, such as tremor and Parkinson's disease may also affect the overall activity level of a patient. Further, movement disorders are also characterized by irregular, uncontrolled and generally inappropriate movements, e.g., tremor or shaking, particularly of the limbs. In addition to using the sensors described above to sense the overall activity level of a movement disorder patient, some embodiments of the invention may use such sensors to detect the types of inappropriate movements associated with the movement disorder. For example, accelerometers, piezoelectric crystals, or EMG electrodes located in the trunk or limbs of a patient may be able to detect inappropriate movements such as tremor. Such detection may also be used to detect epileptic seizures or symptoms of neurological disorders.

Systems according to the invention may periodically determine the level or severity of such movements based on the signals output by such sensors, associate the inappropriate movement levels with current therapy parameter sets, and determine activity metric values for therapy parameter sets based on the associated levels. For example, a processor of such a system may determine a frequency or amount of time that such movements exceeded a threshold during delivery of a therapy parameter set as an inappropriate movement based activity metric value for the therapy parameter set.

Systems according to the invention may include any of a variety of medical devices that deliver any of a variety of therapies to treat a movement disorders (or other neurological disorders), such as DBS, cortical stimulation, or one or more drugs. Systems may use the techniques of the invention described above to associate overall activity levels and metrics, as well as inappropriate movement levels and inappropriate movement activity metrics, with therapy parameter sets for delivery of such therapies. In this manner, such system may allow a user to evaluate the extent to which a therapy parameter set is alleviating the movement disorder by evaluating the extent to which the therapy parameter set improves the overall activity level of the patient and/or decreases the extent of inappropriate movements by the patient.

Although described herein primarily in the context of an implantable neurostimulator, the invention is not so limited. The invention may be embodied in any implantable medical device that delivers a therapy, such as a cardiac pacemaker or an implantable pump. Further, the invention may be implemented via an external, e.g., non-implantable, medical device.

Additionally, the invention is not limited to embodiments in which a programming device receives information from the medical device, or presents information to a user. Other computing devices, such as handheld computers, desktop computers, workstations, or servers may receive information from the medical device and present information to a user as described herein with reference to programmers 20, 26. A computing device, such as a server, may receive information from the medical device and present information to a user via a network, such as a local area network (LAN), wide area network (WAN), or the Internet. Further, in some embodiments, the medical device is an external medical device, and may itself include user interface and display to present activity information to a user, such as a clinician or patient, for evaluation of therapy parameter sets.

As another example, the invention may be embodied in a trial neurostimulator, which is coupled to percutaneous leads implanted within the patient to determine whether the patient is a candidate for neurostimulation, and to evaluate prospective neurostimulation therapy parameter sets. Similarly, the invention may be embodied in a trial drug pump, which is coupled to a percutaneous catheter implanted within the patient to determine whether the patient is a candidate for an implantable pump, and to evaluate prospective therapeutic agent delivery parameter sets. Activity metric values collected during use of the trial neurostimulator or pump may be used by a clinician to evaluate the prospective therapy parameter sets, and select parameter sets for use by the later implanted non-trial neurostimulator or pump. For example, a trial neurostimulator or pump may determine values of one or more activity metrics for each of a plurality of prospective therapy parameter sets, and a clinician programmer may present a list of prospective parameter sets and associated activity metric values to a clinician. The clinician may use the list to identify potentially efficacious parameter sets, and may program a permanent implantable neurostimulator or pump for the patient with the identified parameter sets.

Additionally, the invention is not limited to embodiments in which the therapy delivering medical device monitors the physiological parameters of the patient described herein. In some embodiments, a separate monitoring device monitors values of one or more physiological parameters of the patient instead of, or in addition to, a therapy delivering medical device. The monitor may include a processor 46 and memory 48, and may be coupled to or include sensors 40, as illustrated above with reference to IMDs 14 and FIGS. 2A, 2B, and 4. The monitor may identify activity levels and activity metric values based on the values of the monitored physiological parameter values, or may transmit activity levels or the physiological parameter values to a computing device for determination of the activity metric values.

In embodiments in which the medical device determines activity metric values, the medical device may identify the current therapy parameter set when a value of one or more activity metric values metrics is collected, and may associate that value with the therapy parameter set. In embodiments in which a programming device or other computing device determines activity levels or activity metric values, the medical device may associate recorded physiological parameter values or activity levels with the current therapy parameter set in the memory. Further, in embodiments in which a separate monitoring device records physiological parameter values or determines activity levels or activity metric values, the monitoring device may mark recorded physiological parameter values, activity levels, or activity metric values with a current time in a memory, and the medical device may store an indication of a current therapy parameter set and time in a memory. A programming device of other computing device may receive indications of the physiological parameter values, activity levels, or activity metric values and associated times from the monitoring device, and indications of the therapy parameter sets and associated times from the medical device, and may associate the physiological parameter values, activity levels, or activity metric values with the therapy parameter set that was delivered by the medical device when the values or levels were recorded.

FIG. 9 is a conceptual diagram illustrating a monitor 110 that monitors values of one or more physiological parameters of the patient instead of, or in addition to, a therapy delivering medical device. In the illustrated example, monitor 110 is configured to be attached to or otherwise carried by a belt 112, and may thereby be worn by patient 12C. FIG. 9 also illustrates various sensors 40 that may be coupled to monitor 110 by leads, wires, cables, or wireless connections, such as EEG electrodes 114A-C placed on the scalp of patient 12C, a plurality of EOG electrodes 116A and 116B placed proximate to the eyes of patient 12C, and one or more EMG electrodes 118 placed on the chin or jaw the patient. The number and positions of electrodes 114, 116 and 118 illustrated in FIG. 12 are merely exemplary. For example, although only three EEG electrodes 174 are illustrated in FIGS. 1A and 1B, an array of between 16 and 25 EEG electrodes 114 may be placed on the scalp of patient 12C, as is known in the art. EEG electrodes 114 may be individually placed on patient 12C, or integrated within a cap or hair net worn by the patient.

In the illustrated example, patient 12C wears an ECG belt 120. ECG belt 120 incorporates a plurality of electrodes for sensing the electrical activity of the heart of patient 12C. The heart rate and, in some embodiments, ECG morphology of patient 12C may monitored by monitor 110 based on the signal provided by ECG belt 120. Examples of suitable belts 120 for sensing the heart rate of patient 12C are the “M” and “F” heart rate monitor models commercially available from Polar Electro. In some embodiments, instead of belt 120, patient 12C may wear a plurality of ECG electrodes attached, e.g., via adhesive patches, at various locations on the chest of the patient, as is known in the art. An ECG signal derived from the signals sensed by such an array of electrodes may enable both heart rate and ECG morphology monitoring, as is known in the art.

As shown in FIG. 9, patient 12C may also wear a respiration belt 122 that outputs a signal that varies as a function of respiration of the patient. Respiration belt 122 may be a plethysmograpy belt, and the signal output by respiration belt 122 may vary as a function of the changes is the thoracic or abdominal circumference of patient 12C that accompany breathing by the patient. An example of a suitable belt 122 is the TSD201 Respiratory Effort Transducer commercially available from Biopac Systems, Inc. Alternatively, respiration belt 122 may incorporate or be replaced by a plurality of electrodes that direct an electrical signal through the thorax of the patient, and circuitry to sense the impedance of the thorax, which varies as a function of respiration of the patient, based on the signal. In some embodiments, ECG and respiration belts 120 and 122 may be a common belt worn by patient 12C, and the relative locations of belts 120 and 122 depicted in FIG. 9 are merely exemplary.

In the example illustrated by FIG. 9, patient 12C also wears a transducer 124 that outputs a signal as a function of the oxygen saturation of the blood of patient 12C. Transducer 124 may be an infrared transducer. Transducer 124 may be located on one of the fingers or earlobes of patient 12C. Sensors 40 coupled to monitor 110 may additionally or alternatively include or be coupled to any of the variety of sensors 40 described above with reference to FIGS. 2A and 2B that output signals that vary as a function of patient activity, such as EMG electrodes, accelerometers, piezoelectric crystals, or pressure sensors.

FIG. 10 is a conceptual diagram illustrating a monitor that monitors values of one or more accelerometers of the patient instead of, or in addition to, such monitoring being performed by a therapy delivering medical device. As shown in FIG. 10, patient 12D is wearing monitor 130 attached to belt 132. Monitor 130 is capable of receiving measurements from one or more sensors located on or within patient 12D. In the example of FIG. 10, accelerometers 134 and 136 are attached to the head and hand of patient 12D, respectively. Accelerometers 134 and 136 may measure movement of the extremities, or activity level, of patient 12D to indicate when the patient moves. Alternatively, more or less accelerometers or other sensors may be used with monitor 130. The movement may be an activity event or other movement that is used to determine an activity metric.

Accelerometers 134 and 136 may be preferably multi-axis accelerometers, but single-axis accelerometers may be used. As patient 12D moves, accelerometers 134 and 136 detect this movement and send the signals to monitor 130. High frequency movements of patient 12D may be indicative of tremor, Parkinson's disease, or an epileptic seizure, and monitor 130 may be capable of indicating to an IMD 14, for example, that stimulation therapy must be changed to effectively treat the patient. In addition, accelerometers 134 and 136 may detect the activity of patient 12D in addition to or instead of other sensors 40. Accelerometers 134 and 136 may be worn externally, i.e., on a piece or clothing or a watch, or implanted at specific locations within patient 12D. In addition, accelerometers 134 and 136 may transmit signals to monitor 130 via wireless telemetry or a wired connection.

Monitor 130 may store the measurements from accelerometers 135 and 136 in a memory. Monitor 130 may analyze the measurements using any of the techniques described herein. In some examples, monitor 130 may transmit the measurements from accelerometers 134 and 136 directly to another device, such as an IMD 14, programming device 20,26, or other computing device. In this case, the other device may analyze the measurements from accelerometers 134 and 136 to detect efficacy of therapy or control the delivery of therapy.

In some examples, a rolling window of time may be used when analyzing measurements from accelerometers 134 and 136. Absolute values determined by accelerometers 134 and 136 may drift with time or the magnitude and frequency of patient 12D movement may not be determined by a preset threshold. For this reason, it may be advantageous to normalize and analyze measurements from accelerometers 134 and 136 over a discrete window of time. For example, the rolling window may be useful in detecting epileptic seizures. If monitor 130 or an IMD 14 detects at least a predetermined number of movements over a 15 second window, an epileptic seizure may be most likely occurring. In this manner, a few quick movements from patient 12D not associated with a seizure may not trigger a response and change in therapy. The rolling window may also be used in detecting changes in activity with accelerometers 134 and 136 or other sensors as described herein.

FIG. 11 is a flow diagram illustrating monitoring the heart rate and breathing rate of a patient by measuring cerebral spinal fluid pressure. As discussed above, a physiological parameter that may be measured in patient 12D is heart rate and respiration, or breathing, rate. As shown in FIG. 11, cerebral spinal fluid (CSF) pressure may be analyzed to monitor the heart rate and breathing rate of patient 12D. A clinician initiates a CSF pressure sensor to being monitoring heart rate and/or breathing rate (154). Alternatively, the CSF pressure sensor may be implanted within the brain or spinal cord of patient 12D to acquire accurate pressure signals. The CSF pressure sensor must also store the pressure data or begin to transfer pressure data to an implanted or external device. As an example used herein, the CSF pressure sensor transmits signal data to an IMD 14.

Once the CSF pressure sensor is initiated, the CSF pressure sensor measures CSF pressure and transmits the data to IMD 14 (156). An IMD 14 analyzes the CSF pressure signal to identify the heart rate (158) and breathing rate (160) of patient 12D. The heart rate and breathing rate can be identified within the overall CSF pressure signal. Higher frequency fluctuations (e.g. 40 to 150 beats per minute) can be identified as the heart rate while lower frequency fluctuations (e.g. 3 to 20 breaths per minute) in CSF pressure are the breathing rate. An IMD 14 may employ filters, transformations, or other signal processing techniques to identify the heart rate and breathing rate from the CSF pressure signal.

An IMD 14 may utilize the heart rate and breathing rate information as additional information when determining the activity metric of patient 12D (162). For example, faster heart rates and faster breathing rates may indicate that patient 12D is standing or active. An IMD 14 may then store the activity metric or use it to adjust stimulation therapy (164).

Various embodiments of the invention have been described. However, one skilled in the art will recognize that various modifications may be made to the described embodiments without departing from the scope of the invention. For example, the invention may be embodied as a computer-readable medium that includes instructions to cause a processor to perform any of the methods described herein. These and other embodiments are within the scope of the following claims. 

1. A method comprising: monitoring a signal that varies as a function of patient activity; periodically determining an activity level of the patient based on the signal; associating each of the determined activity levels with a therapy parameter set currently used by a medical device to deliver a therapy to a the patient when the activity level is was determined, wherein the therapy comprises at least one of a movement disorder therapy, psychological disorder therapy, or deep brain stimulation; and determining a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets.
 2. The method of claim 1, wherein determining a value of an activity metric comprises determining at least one of a mean and a median of activity levels associated with the therapy parameter set.
 3. The method of claim 2, wherein determining a value of an activity metric comprises: comparing the at least one of the mean and the median activity level to at least one threshold; and selecting the activity metric value from a plurality of predetermined possible activity metric values based on the comparison.
 4. The method of claim 1, wherein determining a value of an activity metric for a therapy parameter set comprises: comparing each of the activity levels associated with the therapy parameter set to a threshold value; and determining at least one of a percentage of time above the threshold and a percentage of time below the threshold.
 5. The method of claim 1, wherein determining a value of an activity metric for a therapy parameter set comprises: comparing each of the activity levels associated with the therapy parameter set to a threshold value; and determining an average length of time that consecutively determined activity levels associated with the therapy parameter set were above the threshold.
 6. The method of claim 1, wherein determining an activity metric value for each of a plurality of therapy parameter sets comprises determining an average number of activity counts per a unit of time for each of the plurality of therapy parameter sets based on a number of activity counts associated with each of the therapy parameter sets.
 7. The method of claim 1, further comprising presenting a list of the plurality of therapy parameter sets and activity metric values associated with the therapy parameter sets.
 8. The method of claim 7, further comprising ordering the list of therapy parameter sets according to the associated activity metric values.
 9. The method of claim 8, wherein determining a value of an activity metric comprises determining a value of each of a plurality of activity metrics for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets, and ordering the list comprises ordering the list according to a user selected one of the activity metrics.
 10. A medical system comprising: a medical device that delivers at least one of a movement disorder therapy, psychological disorder therapy, or deep brain stimulation to a patient; and a processor that monitors a signal that varies as a function of patient activity, periodically determines an activity level of the patient based on the signal, associates each of the determined activity levels with a therapy parameter set used by the medical device to deliver the at least one of the movement disorder therapy, psychological disorder therapy, or deep brain stimulation to the patient when the activity level was determined, and determines a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets.
 11. The medical system of claim 10, wherein, for each of the therapy parameter sets, the processor determines at least one of a mean and a median of activity levels associated with the therapy parameter set.
 12. The medical system of claim 11, wherein, for each of the therapy parameter sets, the processor compares the at least one of the mean and the median activity level to at least one threshold, and selects an activity metric value from a plurality of predetermined possible activity metric values based on the comparison.
 13. The medical system of claim 10, wherein, for each of the therapy parameter sets, the processor compares each of the activity levels associated with the therapy parameter set to a threshold value, and determines as the activity metric value for the therapy parameter set at least one of a percentage of time above the threshold and a percentage of time below the threshold.
 14. The medical system of claim 10, wherein, for each of the plurality of parameter sets, the processor compares each of the activity levels associated with the therapy parameter set to a threshold value, and determines as the activity metric value for the parameter set an average length of time that consecutively determined activity levels were above the threshold.
 15. The medical system of claim 10, wherein an activity level comprises a number of activity counts, and the activity metric value for each of the therapy parameter sets comprises an average number of activity counts per a unit of time.
 16. The medical system of claim 10, further comprising a programming device that includes a display to present a list of the plurality of therapy parameter sets and activity metric values associated with the therapy parameter sets.
 17. The medical system of claim 16, wherein the programming device orders the list of therapy parameter sets according to the associated activity metric values.
 18. The medical system of claim 17, wherein the processor determines a value of each of a plurality of activity metrics for each of the plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets, and the programming device orders the list according to a user selected one of the activity metrics.
 19. The medical system of claim 10, wherein the medical device comprises an implantable medical device.
 20. The medical system of claim 10, wherein the medical device comprises at least one of an implantable neurostimulator or an implantable pump.
 21. A medical system comprising: means for delivering at least one of a movement disorder therapy, psychological disorder therapy, or deep brain stimulation to a patient; means for monitoring a signal that varies as a function of patient activity; means for periodically determining an activity level of the patient based on the signal; means for associating each of the determined activity levels with a therapy parameter set used by the means for delivering to deliver the at least one of the movement disorder therapy, psychological disorder therapy, or deep brain stimulation to the patient when the activity level was determined; and means for determining a value of an activity metric for each of a plurality of therapy parameter sets based on activity levels associated with the therapy parameter sets. 